Furnace



K. A. LANG Jan. 2, 1968 FURNACE 2 Sheets-Sheet l Filed April l2, 1965Jan. 2, 1968 K. A. LANG FURNACE Filed April l2, 1965 2 Sheets-Sheet 2 I1\" VENTOR United States Patent O 3,361,863 FURNACE Karl A. Lang, 136Venetia Drive, Long Beach, Calif. 90803 Filed Apr. 12, 1965, Ser. No.447,343 Claims. (Cl. 13-25) ABSTRACT OF THE DISCLOSURE A diffusionfurnace structure having a cabinet which supports stacked modules, eachof which includes a drawer tray carrying an elongated capsule enclosinga heating element, the element being electrically connected to thefurnace controls such that the element can be quickly disconnected fromthe cabinet when the tray is opened; and a plurality of metal leavesconstituting a part of the electrical connectors for a heating element,and which are bendable to facilitate axial removal of the elementthrough the opening in either of the ends of an elongated diffusionfurnace capsule or the like.

This invention relates to furnace structures, and more particularly toimprovements in idiffusion furnaces.

More specifically, this invention relates to the type of furnace whichutilizes an elongated heating coil surrounded by a tube of refractorymaterial. In this type of furnace, thick metal straps are welded to theends of the coil for connection to a current source. Additionally, thecoil is tapped by welding additional straps to selected turnsintermediate its ends. Such :additional straps are also adapted to besupplied with heating currents from the source to permit the interior ofthat portion of the coil intermediate the tapped connections to beselectively raised to a higher temperature than that which would beobtained by currents applied through the end connections alone.

Typically, such furnaces are operated with a hollow quartz tube insertedin the heating coil and extending the length thereof. One end of thequartz tube is capped, and materials to be heated in the furnace, suchas semiconductor materials and the like, are inserted into the open endof the `quartz tube.

In such furnaces as heretofore known, all of the metal straps are ledthrough one end of the furnace, where connections are made to the sourceof current. Thus, the strap at one end of the furnace is a short elementextending through the adjacent end of the furnace, whereas the strap atthe opposite end is a member which extends the length of the coil to theend of the furnace Where the connections aremade to the source.Similarly, the straps for the tapped connections are of differentlengths. The reason for this arrangement is to facilitate the removal ofthe heating coil from one end of the furnace when it is necessary -forsuch coil to be replaced.

In this latter connection, the ends of the straps extending out of thefurnace are bent outwardly to permit them lto be-secured to .terminalblocks to which connections from the current source are made. The strapsthemselves are ofrelatively large stock, being of the order of an eighthof an inch thick and up to an inch wide, which necessitates their beingpreformed with the bends in them before they are welded to the heatingcoil. Accordingly, if these straps were led out ,of the opposite ends ofthe furnace, they could not be bent straight to permit the heating coilto be removed from either end of the furnace.

In addition to the foregoing, such prior art furnaces do not lendthemselves to ready replacement of heating elements incertainvenvironments, such as so-called clean rooms, in which it isessential to eliminate all possible dirt from the surrounding air. Suchfurnaces are built in large, heavy supporting structures, and areexpensive. Since a heating element cannot be removed from a furnacewithout releasing particles of refractory material in the surroundingair, its replacement in such surroundings cannot -be tolerated. Rather,it is necessary to remove the entire furnace support structure from thearea in order to make the necessary change, and bring it back in afterthe change is made.

Such operations involve considerable labor and eX- pense, and keep thefurnace out of commission for an undesirably long period of time.Frequently, in order to keep a production line going, a complete furnaceand support structure must be installed in place of the one beingserviced.

It is an object of my invention to provide an improved furnace structurewhich overcomes the above and other disadvantages of the prior art.

Another object of my invention is to provide a diffusion furnace inwhich strap connections to different points on the heating coil can beled out of the ends of the furnace nearest their connections, and stillpermit the heating coil to be removed from either end of the furnace.

A further object of my invention is to provide an improved furnacestructure in the form of a portable cartridge unit containing theheating coil, and which can readily be removed from a supportingstructure and carried out of a work area when it is necessary to replacethe heating element.

Yet another object of my invention is to provide .a furnace structure inwhich individual port-able furnace units of light weight can be arrangedin a stack, but wherein each is separately and easily removable from thestack to permit it to be replaced with a similar unit.

It is also an object of my invention to provide a unique diffusionfurnace, comprising a minimum number of component parts of simple designand rugged construction.

The above and other objects and advantages of my invention will become`apparent from the following description taken in conjunction with theaccompanying drawings of an illustrative embodiment thereof, in which:

FIGURE l is a perspective View of a furnace structure in which a pair ofreplaceable cartridge heating assemblies are arranged in a stack on abase cabinet structure which houses controls for the heating elements inthe heating assemblies, each heating assembly being located in arespective cabinet module, with one of the modules having its frontpanel removed and the cartridge therein moved to the exterior by meansof the drawer mechanism on which it is carried;

FIGURE 2 is a fragmentary sectional view taken along the line 2--2 ofFIGURE l, showing the internal constructions for the cartridge units;

FIGURE 3 is an end view of the tube of refractory material in which theheating coil is mounted;

FIGURE 4 is an enlarged side elevation view of the heating coil with themetal straps Welded thereto extendling in opposite directions past theends of the coil, and showing the plurality of metal leaves welded tothe ends of the straps for connection to exterior terminal blocks;

FIGURE 5 is an exploded view of the elements of a terminal block;

FIGURE 6 is an enlarged sectional View of one of the terminal blocksmounted over a slot in the end of the cartridge housing, showing moreclearly the manner in which the metal leaves welded to one of the strapconnections to the heating coil are directed through the slot in thehousing and secured to the terminal block; and

FIGURE 7 is a sectional view taken along the line 7-7 of FIGURE 6,showing the portions of the metal strap and the metal leaves where theyare welded together'.

Referring to FIGURE 1, the furnace structure is formed of a base cabinet11 on top of which is supported a stack of pairs of cabinet modules 12,13 which support individual cartridge heating assemblies. The modules12, 13 are identical in construction, each being provided with a frontpanel, as indicated at 14 for themodule 13, which can readily beattached to and removed from the front of the module. Within each moduleis a cartridge heating assembly 15 which has an elongated housing 16that sets in a drawer tray 17. The tray 17 is adapted to be pulled out asufficient distance to permit the housing 16 to be lifted out of thetray for servicing and/ or replacement. As indicated, the tray 17 isprovided with side bars 18 slidably mounted in channels 19 which aresecured to the sides of the module 12. The bars 18 may be adapted toglide on suitable bearings within the channel 19 in the manner employedin conventional drawer constructions for ling cabinets and the like.

Each cartridge assembly 15 is a complete furnace unit. Referring toFIGURE 2, the housing 16 is formed of a cylindrical tube 20 having endcaps 21, 22 having aligned central openings 23, 24. Extending throughthe center of the housing is a tube of refractory material Within whichis an elongated heating coil 26. Preferably the tube 25 is formed withan interior groove to nestably receive the outer portions of the turnsof the coils, wherebythe internal rib, indicated at 27, extends betweenthe turns ofthe coil.

Referring to FIGURE 3 along with FIGURE 2, the refractory tube 25 isformed of two semcylindrical sections 28, 29. In assembly, the sections28, 29 are placed around the heating coil 26, as by laying the coil inone section with its turns nested in the grooves of that section, andthen placing the other section over the exposed portion of the coil withthe turns of the coil located in the grooves of that section.

Preparatory to assembling the coil 26 in the refractory tube 25 (seeFIGURES 2.-4), metal straps are welded to the coil. In this connection,a pair of relatively short metal straps 31, 32, of the order of four orlive inches in length, are welded to the end turns of the coil 26.Additional straps 33, 34- which are several inches longer than the endstraps are welded to respective turns of the coil a few inches from eachthereof. As shown, the inner ends of the straps 33, 34 are bentinwardly, whereby the main bodies of the straps are spaced from thecoil. The sections 28, y29 of the refractory tube 25 are formed withnotches 36, 37 in the confronting edge portions thereof to form slotsfor the bent ends of the straps 33, 34. The bottom surfaces of these-straps thus rest on the outer surface of the refractory tube 25.

This type of heating unit is one which is adapted to heat the interiorof the coil 26 to extremely high temperatures, e.g., of the order of2.,500 F. which lrequires that the coil be formed of relatively thickstock, e.g., wire of the order of a quarter of an inch in diameter, andmetal straps for connection to a current source of upwards to an inch inwidth and an eighth of an inch or more in thickness. With straps of suchdimensions, it is necessary to preform them with the bends in the endsthereof that are welded to the coil, as by heating the stock to a hightemperature and hammering it into the desired shape.

Also as indicated, the practice heretofore has been to form the outerends of the straps with bends in them, the straps being of sufficientlength that the bend ends extend out of the furnace to points Where theymay be connected to a, current source. As explained, such a structurerequires that all the straps be led out of the furnace at one end of thecoil, so that the coil could be removed from that end of the furnace forreplacement.

However, with my invention it is possible to remove the coil from eitherend of the furance when it is necessary that it be replaced. To thisend, the ends of the straps extending past the opposite ends of the coil26 are not formed with any bends therein, but there is welded to theouter end of each strap 31-34 a stack of a plurality of elongated metalleaves 31-34. With reference to FIGURE 7, the edges of the stack ofleaves 31 are welded together at one end and to the one surface of theend of the strap 31, as indicated at 35. Preferably, these elements arewelded together so that the welds 35 are formed of parent metal, such asby the heliarc welding technique.

After the metal straps 31-34 are welded to the heating coil 26, and thestacks of metal leaves 31-34 are welded to the outer ends of the metalstraps 31-34, the sections of the refractory tube 25 are placed aroundthe coil and inserted in a surrounding tube 37 of refractory material.The tube 37 is substantially coextensive with the tubey 25, and issupported within the housing 16 by surrounding bands 38-40 of heatinsulation (eg. rock wool or the like) and refractory materials. Theannular spaces between the ends of the bands 38-40 and the inner wallsof the caps 21, 22 are filled With rings 41 of suitable refractorymaterial.

After sliding the assembly of the refractory tube and heating coil 2,6inside the tube 37, the stacks 'of metal leaves 31-34 are led out of theopposite ends of the housing 1-6 and clamped to electrical terminalblocks 44. Referring to FIGURES 5 and 6 along with FIGURES 1 and 2, therespective slots 45 for each of the stacks of leaves 31-34 are formed inthe end caps 21, 22 of the housing 16, each slot 45 extending outwardlyfrom the central openings 23, 24. Additionally, the pair of slots 45 ineach end of the housing are located in the forward portions of thoseends, i.e., nearest the front of the cabinet module. In this connection,it will be observed that the straps at each end are welded to portionsof the coil that are angularly displaced. Accordingly, the slots 45 aresimilarly displaced in the ends of the housing.

Referring to FIGURES 2, 5 and 6, each terminal block 44 is formed of alrigid rectangular block 50 of electrical insulation which on its lowersurface is provided with a downwardly extending projection 50' extendingpart Way along its length of one end thereof, and which is adapted to beinserted in the slot 45. The block 50 has a rectangular opening 5,1which extends through the bottom projection 50. Additionally, the block50 is provided with a pair of upwardly projecting threaded bolts 5 2,the heads of which (see FIGURE 6) are located in countersunk openings-of sufficient size that the lower surfaces of the heads are above theplane of the lower surface of the block. The bolts 52 may be embedded inthe block or, as indicated, secured in place by nuts 53 threaded thereonto tightly engage the upper surface of the block.

As shown,'the block 5,0 is kept out of contact with the surface of theend cap 21 by a strip 54 of heat insulation, which may be made ofasbestos or the like. The insulation strip 54 is a rectangular elementof the outer dimensions of the block 50 having a slot 54 therein of thedimensions of the slot 45. The block 50 is secured to the end carp 21,with the insulation strip 54 sandwiched therebetween, in any suitablemanner, e.g., as by nut and bolt connections 55.

Preparatory to securing the block 50 in place, the stack of metal leavesare threaded through the slot 45 and the opening 51 in the block 50.Thereafter, the block is lowered along the leaves to be seated againstthe outer surface of the end cap 21 and secured in place. Referring toFIG- URE 6, the grouped metal leaves 31 are then bent and placed overthe upper surface of a conductor plate 58 which is supported at one endon the threaded ends of the bolts 52, such bolts extending throughopenings 59 (see FIGURE 5) in the plate. Then a metal strip`60 havingopenings 61 aligned with the bolts 52 is lowered onto the bolts againstthe outer leaf Iof the stack 31', and nuts 62 are threaded onto theupper ends of the bolts A52 and tightened securely to compress theleaves into firm faceto-,face contact With each other and insure rrnface-toface contact between the bottom leaf of the stack and the uppersurface of the conductor plate 58.

With the terminal blocks 44 secured to the ends of the housing 16, thecartridge unit 15 is ready for mounting in the cabinet module 12. It isplaced in the tray 17, which has been pulled forward to the exterior ofthe cabinet, and with the terminal blocks 44 located in the forwardpositions as shown in FIGURE l. Before the tray 17 is shoved inwardly,electrical connections within the base cabinet prtion 11 are connectedto the terminal blocks 44. To this end, and referring to FIGURES 2 and6, each conductor plate 58 extends past the outer end of the insulationblock 50, and is provided with an opening 63 to receive the threaded endof a bolt 64 on which the lug 65 of an insulated conductor 66 is placed.A nut and washer combination 67, 68 are placed over the upper end of thethreaded bolt 64, and the nut turned on the bolt until the lug 65 issecurely clamped to the conductor plate 58.

After the conductors 66 are connected to the terminal blocks 44, thetray 17 is moved inwardly to position the capsule inside the cabinetmodule 12. When this is done, the openings 23, 24 in the ends of thehousing 16 are brought into alignment with enlarged openings 70 in theends of the cabinet. Referring to FIGURE 2, alongpwith FIGURE l, an endplug 71 of refractory material is inserted in the opening 70. The outerdiameter of the plug 71 is only slightly less than the diameter of theopening 24 in the end cap 22, so that it can readily pass through thatopening. The plug 71 at its inner end has a reduced diameter, indicatedat 72, and at its inner end the plug abuts the end of the refractorytube in which the heating coil 26 is located. As shown, the plug 71 isnotched at its inner end, as indicated at 73, to provide a passage forthe stack of metal leaves 34', to facilitate leading the stack of leavesto the exterior of the housing with a minimum of bending.

After the plug 71 is inserted in each end of the housing, a sealing ring74 of suitable heat insulation material, such as asbestos rope, isplaced around the axial lip or flange 75 which defines the end opening24 of the housing 16. Thereupon, a short cylindrical element 77 isinserted in the opening 70 of the cabinet 13, such element 77 having anexternal flange 78 which fits against the outer surface of the cabinet13. The inner end of the element 77 is curved or flared slightly, andengages the sealing ring 74. The flange 78 is secured to the wall of thecabinet 13, as by means of a trim plate 81 placed around the flange, andwith nut and bolt connections 82, S3 for clamping the -flange 78 betweenthe plate 81 and the wall of the cabinet 13. Thus clamped, the inner end79 of the cylindrical element 77 firmly engages the sealing ring 74 andpresses it against the end cap 22. Thereafter, the front panel 14 issecured in place.

With the furnace capsule 15 thus completed, it is ready for use. In suchuse, a conventional quartz tube 85 (see FIGURE 2) is extended throughthe cabinet from end to end. The ends yof the quartz tube 85 aresupported by the refractory plugs 71 and the outside trim plates 81,such elements for this purpose being provided with internal openings toslidably receive the quartz tube.

With the above-described arrangement for clamping the ends of thehousing 16 in place, the cartridge 15 cannot readily be dislodged fromoperating position, as upon opening the front panel and inadvertentlypulling on the tray 17. Before the tray can be pulled out, and pull thecartridge 15 with it, the end clamping elements 7\7 have to be removed,along with the end refractory plugs 71. Also, of course, the quartz tubeS5 must be removed. However, the operations for removing these elementscan be seen to be easy to accomplish, and can be done in a minimum oftime when it is desired to service or replace the cartridge 15.

To remove the heating element itself, it is necessary only to remove theouter trim plates 81, the clamping cylinder 77 and the refractory plug71 as above described, and to pull the tray 17 out. The conductors 66are then removed from the conductor plates 58, and the stacks of leaves31'-34 are unclarnped from the conductor plates. Since the leaves of thestacks 3134 are relatively thin members, being formed of, for example,elements of the order of .025-inch thickness, they can readily be bentinwardly to clear the opening in the supporting refractory tube 37.Since the interior of the supporting tube 37 is equal to the outerdiameter coil-supporting tube 25 and the thickness of one of the straps33, 34, the unit assembly of the heating coil with its straps andsupporting tube 25 is easily slidable in the support tube 37, and caneasily be pulled out of either end of the support tube 37.

After removal of the heating unit as above described, a replacement unitof the same construction can be slidably inserted in the support tube37. In this connection, it will be understood that the entire terminalblock assemblies 44 are removed in order to facilitate bending thestacks of leaves 31'-34 inwardly as described for easy removal of theheating unit. When a new unit is positioned in the support tube 37, thestacks of leaves welded to the metal straps thereof are forced outwardlythrough the slots 45, and the terminal blocks assembled as in the mannerpreviously described.

The above-described operations for replacing the heating unit while thehousing 16 remains in the tray 17 may not be permitted in an area wherethe dust from the refractory material cannot be allowed to enter thesurrounding air. In that case, since the housing 16 merely sets in thetray 17, the entire cartridge 15 can be lifted out of the tray andremoved from the area while the heating unit is being replaced.

Still further, if production operations must be continued while aheating unit is being replaced, it is a simple matter to lift the entirecartridge unit 15 from the tray 17, replace it with another completecartridge, making the necessary connections for the conductors, andquickly installing the new cartridge in place. Then the cartridge thathas been replaced can be taken out of the area and its heating unitreplaced, whereby it is available as a standby cartridge for usewhenever it is needed.

From the foregoing, it will be apparent that modications can be made invarious parts of the invention illustrated and described herein wit-houtdeparting from its spirit and scope. Accordingly, I do not intend thatmy invention be limited, except as by the appended claims.

I claim:

1. Furnace apparatus comprising:

an elongated housing having end -walls with central openings therein;

a body of refractory material supported in said housing and having acylindrical opening aligned with said central openings;

an elongated heating coil extending through the opening in said body;

a respective rigid metal strap welded to each end of said coil, saidstraps extending parallel to said axis;

a respective stack of elongated metal leaves welded at one end to theouter end of each strap, said stacks at their opposite ends extendingthrough the central openings in said end walls, the outer ends of saidstacks being bent outwardly, said outer ends being bendable inwardly topermit said coil to be removed through either end of said body andhousing;

and respective electrical terminal means insulatingly and releasablysupporting said outer end of said stacks against said end wa-lls.

2. Furnace apparatus as dened tap connections to turns of the coilinwardly of the ends thereof, said connections being formed of rigidmetal straps extending parallel to said coil past the opposite endsthereof;

a pair of elongated stacks of metal leaves each welded at one end to theouter end of one of the last-mentioned metal straps, said metal leavesbeing bent outwardly and bendable inwardly in the same manner as thefirst-mentioned stacks;

in claim 1, including and respective electrical terminal meansinsulatingly and releasably supporting the outer ends of saidlastmentioned stacks against said end walls.

3. Furnace apparatus as defined in claim 2, including a tube ofrefractory material within the cylindrical opening in said body, saidtube enclosing said coil, said tube being formed of semicylindricalsections, said straps forming the tap connections extending along theouter surface of said tube, the inner ends of such straps being bentinwardly and extending through said tube` 4. Furnace apparatus asdefined in claim 3, including a plug of refractory material filling theopening in each end wall of said housing and abutting the adjacent endof said tube, said plugs having central openings to slidably receive andsupport the ends of a quartz tube extending through the center of saidcoil.

5. Furnace apparatus as defined in claim 4, including a cabinet havingend walls with openings therein and spaced from the end walls of saidhousing, said plugs extending substantially to the end walls of saidcabinet;

and means for releasably clamping said housing between the end walls ofsaid cabinet.

6. Furnace apparatus as defined in claim 5, including a tray in thebottom of said cabinet and slidable to the exterior thereof, and saidhousing being supported in said tray.

7. In combination:

an elongated heating coil;

a pair of axially directed, rigid metal straps welded to the ends of thecoil;

additional rigid metal straps welded to the turns of the coilintermediate the ends thereof, each of said additional straps extendingin opposite directions along said coil and past the ends thereof;

and a respective stack of elongated metal leaves welded together at oneend and to the outer endof each metal strap.

8. The combination defined in claim 7,

said additional straps being pre-formed with bends in the end thereofthat are welded to the coil turns, whereby such straps are spaced fromsaid coil;

and a tube of refractory material surrounding said coil,

said additional straps extending along the outer surface of said tube,the bent ends of said straps extending through the wall of said tube.

9. A furnace structure comprising:

a base cabinet housing electric controls for respective furnace heatingunits;

cabinet modules for each unit stacked on said base cabinet, each modulebeing formed as a box having a removable front panel;

an elongated capsule enclosing a heating unit having a heating coil;

a drawer mechanism mounted at the floor of each module and having aslidable tray carrying a respective capsule, said tray being slidable toa closed position in which said capsule thereon is inside its mo'dule,said tray being slidable to an open position in which, when the frontpanel is removed, the capsule thereon is held exteriorly of its module;

electrical connecting means for each coil extending from the basecabinet to each module;

means carried by each capsule for releasably connecting selected pointson each coil to the associated electrical connecting means;

and means for releasably holding each capsule in its module in theclosed position of its tray.

10. A furnace structure as defined in claim 9,

wherein each capsule has openings at the ends thereof,

wherein said releasable connecting means includes respective stacks ofleaf conductor strips welded at one end to a respective rigid metalstrap, each strap being welded to a selected point on its associatedcoil, the outer end of each stack extending through the opening in itscapsule nearest the point of the coil to which it is conductivelyconnected;

and a respective terminal means for releasably and insulatingly holdingthe outer end of each stack to the adjacent end of the capsule, and forconductively connecting a respective electrical connecting means to thestack.

References Cited UNITED STATES PATENTS 1,282,330 10/1918 Van Aller219-390 1,588,556 6/1926 Thompson 339-9 1,930,836 10/1933 DArnico219-390 2,527,026 10/1950 Macher 338-323 2,535,379 12/1950 White 219-403X 3,178,665 4/1965 Matheson et al 338-299 3,299,196 1/1967 Lasch et al.13-24 FOREIGN PATENTS l 877,776 9/1961 Great Britain. 930,298 8/1947France.

RICHARD M. WOOD, Primary Examiner.

VOLODYMYR Y. MAYEWSKY, Examiner.

